This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9904240-0 filed in Sweden on Nov. 23, 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to a cover element, such as a module lid, e.g. a DC/DC-module lid, and then preferably a cover element or lid for a BGA-type DC/DC-module.
In this document, a DC/DC-module is a direct current converter which is intended to be mounted on a circuit board and which may, itself, comprise a number of smaller components. A comparison is often made between the cost of a module and the cost of the components corresponding to a module if they were mounted directly on a user circuit board. The introduction of surface mounting of modules has resulted in greater demands on the temperature durability of the finished product and the precision of the terminal leads.
Ball Grid Array (BGA) type capsules are a type of capsule or can which are often used for logic circuits and which includes many inputs and outputs, This type of capsule is comprised essentially of carrier parts on which one or more chips are mounted. The upper side of the carrier on which the chip is mounted is usually moulded in a plastic material, for instance an epoxy resin. The underside of the carrier includes terminals that consist of hundreds of solder balls or bumps, which have obtained their form through natural processes when re-melting. When a BGA-type capsule, or xe2x80x9cdaughter boardxe2x80x9d, is placed on a xe2x80x9cmother boardxe2x80x9d and heated in a remelt oven, the balls melt and wet a corresponding surface on the mother board. The wetting forces ensure that the capsule will not drop too far. A BGA capsule eliminates several of the drawbacks of conventional capsules or cans. A BGA capsule has no terminal leads. Any non-flatness is compensated for by virtue of the capsule falling d own onto the mother board, and no complicated lead bending operations are required.
In order to simplify the manufacturing of a DC/DC-module, the material used and the manufacturing steps entailed have been minimized with respect to the components necessary for the module, where a DC/DC-module does not require as many input and output signals as a standard BGA-type module. The use of the same basic construction as that of a BGA-type module while building a compete subsystem on the module, in this case a DC/DC-module, would give essentially the same advantages as those afforded by the BGA capsule mentioned above.
In order to further simplify the manufacturing and handling of the DC/DC-module, the module has been provided with a lid. The main purposes of the module lid is to provide a surface for vacuum-plucking of the module, to provide a surface for marking the module, and also to afford mechanical protection when manually handling the module. The lid includes partially open sides through which cool air is able to pass around the module components and which enables washing and rinsing liquids to be evacuated from the module.
When heating DC/DC-modules of the so-called BGA-type that are baked in plastic, moisture may be released from the module board during the process of melting the solder bumps with the intention of achieving connections with underlying contact elements and blow apart the plastic casing. The open construction provided by a lid that has open sides in accordance with the invention enables the module board to be ventilated and therewith eliminate this problem.